1. Field of the Invention
The present invention relates to a linear guide mechanism of a lens barrel.
2. Description of the Related Art
In lens barrels such as those for cameras, it is often the case that an optical element holding member which holds an optical element such as a lens group is moved in an optical axis direction by a combination of a linear guide mechanism for guiding the optical element holding member linearly in the optical axis direction and a rotatable ring such as a cam ring. An example of such a lens barrel is disclosed in Japanese Unexamined Patent Publication 2004-151710.
A typical linear guide mechanism of a lens barrel is structured by providing a linear guide member (such as a linear guide ring) with a set of guiding portions such as elongated grooves or guide keys, each of which includes a guide surface extending in an optical axis direction, and by providing a linearly movable member (such as a linearly movable ring) with a corresponding set of slide portions which are in slidable contact with the set of guide surfaces. The maximum amount of movement of the linearly movable member is determined by the length of the set of guide surfaces on the linear guide member, and this length is restricted by the length of the linear guide member in the optical axis direction. Namely, in the related art, it is impossible to make the range of movement of the linearly movable member greater than the length of the linear guide member in the optical axis direction, and accordingly, an enlarged range of movement of the linearly movable member and miniaturization of the linear guide member in the optical axis direction are traded off for each other. For instance, in a zoom lens, if it is attempted to increase the range of movement of each movable lens group in the optical axis direction to achieve a high zoom ratio, the linear guide member for this movable lens group increases in size in the optical axis direction, thus restricting the miniaturization of the lens barrel, especially in the optical axis direction. Conversely, if the linear guide member is small (short) in the optical axis direction, the linearly movable member cannot be made to have a wide range of movement in the optical axis direction.